Typically, when a film is produced, duplicate negatives are also created from the original negative. One method of negative duplication involves producing an interpositive element, in which the original negative is contact-printed onto film to produce a positive image on film (an interpositive). The interpositive is then contact-printed onto film to produce the duplicate negative (internegative). This process provides the most accurate tone reproductions possible, and results in two duplicates for relatively little additional cost. The two copies produced are the interpositive, which becomes the master, and the internegative, which becomes the use copy.
However, the production of these intermediate film elements (interpositive and internegative) further makes possible their unauthorized or unwanted reproduction. Such elements may be copied illicitly, in violation of the proprietors' copyrights, and it is often difficult for proprietors to tracks the uses to which their film is put.
Accordingly, an efficient and effective method for detecting and tracing unauthorized copying of a film element would be highly desirable.